Group 13 Elements General Introduction – Electronic configuration and general trends in physical and: NEET MCQs with Answers

15 free questions on Group 13 Elements General Introduction – Electronic configuration and general trends in physical and for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Electronic configuration and general trends in physical and chemical properties of elements across the periods and down the groups; unique behaviour of the first element in each group.

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Question 1

Previous-year question
Which of the following statements is incorrect? [NEET 2024 (Sawaimadhopur)]
  1. Boron trioxide is acidic, aluminium and gallium trioxides are amphoteric while indium and thallium trioxides are basic.
  2. The hybridisation of Al in [Al(H₂O)₆]³⁺ is d²sp³.
  3. Two isotopes of boron, namely ¹⁰B (19%) and ¹¹B (81%), are known.
  4. The relative stability of group 13 elements in the +1 oxidation state varies as Al < Ga < In < Tl.
Show answer
Answer: (B) The hybridisation of Al in [Al(H₂O)₆]³⁺ is d²sp³.
Explanation: In [Al(H₂O)₆]³⁺ aluminium uses its 3s, 3p and outer 3d orbitals, so the hybridisation is sp³d², not d²sp³ (Al has no inner d orbitals); that statement is the incorrect one. The oxide trend (B₂O₃ acidic, Al₂O₃ and Ga₂O₃ amphoteric, In₂O₃ and Tl₂O₃ basic), the isotopes ¹⁰B (19%) and ¹¹B (81%), and the +1 stability order Al < Ga < In < Tl are all correct.

Question 2

Previous-year question
Identify the element M whose trihalides cannot undergo hydrolysis to give an ion of the type [M(H₂O)₆]³⁺. [NEET 2023 (Manipur)]
  1. Ga
  2. In
  3. Al
  4. B
Show answer
Answer: (D) B
Explanation: Boron has no d orbitals, so its maximum covalency is 4; it cannot expand its coordination to six. Hence BX₃ cannot form [B(H₂O)₆]³⁺ on hydrolysis, whereas Al, Ga and In, which can use d orbitals, form hexaaqua ions [M(H₂O)₆]³⁺.

Question 3

Previous-year question
Considering stability, which of the following relationships is correct? [NEET 2023]
  1. InI₃ > InI
  2. AlCl > AlCl₃
  3. TlI > TlI₃
  4. TlCl₃ > TlCl
Show answer
Answer: (C) TlI > TlI₃
Explanation: Owing to the inert pair effect, thallium is more stable in the +1 state than in the +3 state, so TlI is more stable than TlI₃ (TlI₃ is actually Tl⁺I₃⁻, not Tl³⁺ with three I⁻). This is the clear-cut correct relationship. Aluminium strongly prefers +3, so AlCl₃ > AlCl, and thallium chlorides follow TlCl > TlCl₃. Indium commonly shows +3, but I⁻ is a reducing anion and InI is itself a well-known stable compound, so InI₃ > InI cannot be stated as clearly.

Question 4

Previous-year question
Which one of the following statements is correct? [NEET 2022 (Overseas)]
  1. Al⁺ is more stable than In⁺
  2. Ga⁺ is more stable than Al⁺
  3. Al⁺ is more stable than Ga⁺
  4. Ga⁺ is more stable than In⁺
Show answer
Answer: (B) Ga⁺ is more stable than Al⁺
Explanation: Due to the inert pair effect, the stability of the +1 oxidation state in group 13 increases down the group: Al < Ga < In < Tl. Thus Ga⁺ is more stable than Al⁺, whereas Al⁺ is less stable than both Ga⁺ and In⁺, and Ga⁺ is less stable than In⁺.

Question 5

Previous-year question
Which one of the following elements is unable to form an MF₆³⁻ ion? [NEET 2018]
  1. Ga
  2. Al
  3. In
  4. B
Show answer
Answer: (D) B
Explanation: Boron has no d orbitals in its valence shell (n = 2) and cannot expand its octet, so its maximum covalency is four. Aluminium, gallium and indium can use vacant d orbitals to reach a coordination number of six.

Question 6

Previous-year question
The correct order of atomic radii of the group-13 elements is [NEET 2018]
  1. B < Al < In < Ga < Tl
  2. B < Al < Ga < In < Tl
  3. B < Ga < Al < In < Tl
  4. B < Ga < In < Al < Tl
Show answer
Answer: (C) B < Ga < Al < In < Tl
Explanation: Radii increase down the group, but gallium is smaller than aluminium because the newly filled 3d¹⁰ electrons shield the nuclear charge poorly. Hence the order is B < Ga < Al < In < Tl.

Question 7

Previous-year question
The stability of the +1 oxidation state among Al, Ga, In and Tl increases in the order [AIPMT 2015]
  1. Ga < In < Al < Tl
  2. Al < Ga < In < Tl
  3. Tl < In < Ga < Al
  4. In < Tl < Ga < Al
Show answer
Answer: (B) Al < Ga < In < Tl
Explanation: Down the group the ns² pair becomes progressively more inert because of poor shielding by the intervening d and f electrons, so the lower (+1) state becomes more stable: Al < Ga < In < Tl. In thallium the +1 state is actually more stable than +3.
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Question 8

Previous-year question
Boric acid is an acid because its molecule: [AIPMT, 2016]
  1. combines with proton from water molecule
  2. contains replaceable H⁺ ion
  3. gives up a proton
  4. accepts OH⁻ from water releasing proton
Show answer
Answer: (D) accepts OH⁻ from water releasing proton
Explanation: Boric acid is a Lewis acid: it accepts OH⁻ from water forming [B(OH)₄]⁻ and releasing H⁺.

Question 9

Previous-year question
The stability of +1 oxidation state among Al, Ga, In and Tl increases in the sequence: [Re-AIPMT, 2015]
  1. Tl < In < Ga < Al
  2. In < Tl < Ga < Al
  3. Ga < In < Al < Tl
  4. Al < Ga < In < Tl
Show answer
Answer: (D) Al < Ga < In < Tl
Explanation: Because of the inert pair effect, the +1 state becomes more stable down the group: Al < Ga < In < Tl.

Question 10

Previous-year question
NO₂ and SO₂ have some properties in common. Which property is shown by one but not the other? [AIPMT, 2015]
  1. is a reducing agent
  2. is soluble in water
  3. is used as a food-preservative
  4. forms 'acid-rain'
Show answer
Answer: (C) is used as a food-preservative
Explanation: Both gases dissolve in water and both contribute to acid rain. SO₂ is used as a food preservative (for example in squashes and jams), whereas toxic NO₂ is not, so this property belongs to only one of them.

Question 11

Previous-year question
Which of the following does not give oxygen on heating? [NEET-UG, 2013]
  1. (NH₄)₂Cr₂O₇
  2. KClO₃
  3. Zn(ClO₃)₂
  4. K₂Cr₂O₇
Show answer
Answer: (A) (NH₄)₂Cr₂O₇
Explanation: (NH₄)₂Cr₂O₇ decomposes to give N₂ (not O₂): (NH₄)₂Cr₂O₇ → Cr₂O₃ + N₂ + 4H₂O.

Question 12

Previous-year question
Match List-I (substance) with List-II (process): A.Sulphuric acid B.Steel C.Sodium hydroxide D.Ammonia; (i)Haber's (ii)Bessemer's (iii)Leblanc (iv)Contact [AIPMT Mains, 2010]
  1. A-i, B-ii, C-iii, D-iv
  2. A-iv, B-iii, C-ii, D-i
  3. A-iv, B-ii, C-iii, D-i
  4. A-i, B-iv, C-ii, D-iii
Show answer
Answer: (C) A-iv, B-ii, C-iii, D-i
Explanation: Sulphuric acid → Contact, Steel → Bessemer, Sodium hydroxide → Leblanc, Ammonia → Haber; i.e. A-iv, B-ii, C-iii, D-i.

Question 13

Previous-year question
Which one of the following molecular hydrides acts as a Lewis acid? [AIPMT Pre, 2010]
  1. CH₄
  2. NH₃
  3. H₂O
  4. B₂H₆
Show answer
Answer: (D) B₂H₆
Explanation: B₂H₆ is electron-deficient and accepts electron pairs, so it acts as a Lewis acid; CH₄ is neutral and NH₃, H₂O are Lewis bases.

Question 14

Previous-year question
Which of the following is not a correct statement? [AIPMT, 2006]
  1. Multiple bonds are always shorter than corresponding single bonds
  2. The electron-deficient molecules can act as Lewis acids
  3. The canonical structures have no real existence
  4. Every AB₅ molecule does in fact have square pyramid structure
Show answer
Answer: (D) Every AB₅ molecule does in fact have square pyramid structure
Explanation: The shape of an AB₅ molecule depends on the lone pairs on A: PCl₅ (no lone pair) is trigonal bipyramidal, while BrF₅ (one lone pair) is square pyramidal. So the claim that every AB₅ molecule is square pyramidal is false.

Question 15

Which statement correctly describes the change in melting point on going down group 13?
  1. It falls from B to Ga and then rises to Tl because the structures of the elements change
  2. It falls steadily from B to Tl because atomic size increases
  3. It rises steadily from B to Tl because atomic mass increases
  4. It rises from B to Al and then falls to Tl because of the inert pair effect
Show answer
Answer: (A) It falls from B to Ga and then rises to Tl because the structures of the elements change
Explanation: The melting point order is B > Al > Tl > In > Ga, so the trend is not regular. Boron has a very high value because of its strong covalent three-dimensional structure, and gallium has an abnormally low value of 303 K. The value rises again after gallium, and the irregularity is due to changes in the structures of the elements.

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